Endobronchial pH. Relevance of aminoglycoside activity in gram-negative bacillary pneumonia

The in vitro bactericidal activity of certain antimicrobials, especially aminoglycosides, is markedly diminished at an acid pH. In an attempt to correlate this factor with the poor response of gram-negative bacillary pneumonia to aminoglycoside therapy, the endobronchial pH of selected groups of subjects was measured via a bronchoscopically directed pH electrode. The average peripheral, i.e., subsegmental, endobronchial pH of normal persons, patients with chronic lung disease, and patients with pneumonia was 6.58 +/- 0.06, 6.62 +/- 0.10, and 6.61 +/- 0.06, respectively. The average central airway, i.e., major bronchi or tracheal, pH at 6.64 +/- 0.07 did not vary significantly from that of peripheral airways. The presence of pneumonia in individual bronchi was associated with a significantly lower pH than that in noninfected bronchi: 6.48 +/- 0.12 versus 6.69 +/- 0.13 (p less than 0.05). This relatively acid environment appears exaggerated within pneumonic airways and may contribute toward decreasing the effectiveness of aminoglycosides and certain other antimicrobials used in treating lung infection.